Mine

   public static boolean verifdiago(char tab[][], int pos, char comparer)
   {
       int lig = 0;
       for(int i = 0; i < tab.length; i++)
           if(tab[i][pos-1] == comparer)
               {
                   lig = i;
                   break;
               }
      pos--;
      int ligDepart = lig;
      int posDepart = pos;
      boolean valide = false;
         
      while (tab[lig][pos]==comparer && pos > 0 && lig > 0) {
         pos--;
         lig--;
      }
      if(pos > 0 && lig+1 < 3 && pos < tab[0].length - 3){
         if(tab[lig+1][pos+1] == comparer && tab[lig+2][pos+2] == comparer && tab[lig+3][pos+3] == comparer){valide = true;}
      }
      else if(pos == 0 && lig < 3 && pos < tab[0].length - 3) {
         if(tab[lig+1][pos+1] == comparer && tab[lig+2][pos+2] == comparer && tab[lig+3][pos+3] == comparer && tab[lig+4][pos+4] == comparer){valide = true;}
      }
      
      pos = posDepart;
      lig = ligDepart;
      while (tab[lig][pos]==comparer && pos > 0 && lig < tab.length-1) {
         pos--;
         lig++;
      }
      if(pos > 0 && lig > 3 && pos < tab[0].length - 3){
         if(tab[lig][pos] == comparer && tab[lig-1][pos+1] == comparer && tab[lig-2][pos+2] == comparer){valide = true;}
      }
      else if(pos == 0 && lig > 3 && pos < tab[0].length - 3) {
         if(tab[lig][pos] == comparer && tab[lig-1][pos+1] == comparer && tab[lig-2][pos+2] == comparer && tab[lig-3][pos+3] == comparer){valide = true;}
      }

      return valide;
   }